Ive had a long running problem with my 2litre 110 HDi Pug 406 Engine Management System. The warning light (K light I beleive its known as) has been pretty well stuck on for over a year and despite several attempts to fix it by two Pug garages, Im now at a point where (I'm told) either the wiring loom or the ECU itself needs replacing - both together are in the order of 1700 pounds. As the car is 6 years old shortly, with 83K on the clock, this is out of the question. Various wiring changes have been made, the fule switch has been chenged a total of three times (certainly at least twice) and various "tweaks" but although the light will go out for a few days (once it stayed off for three weeks!), even today, its back on.

The card drives extremely well however. (Full service history and all that). Apart from, that is, when the engine is very cold (i.e when the outside temp is at 2 degrees celcius or less, when the engines idling speed will rise from arounf 950 to 1100/1200 rpm, and the car can be very sluggish indded (even with the gas pedal on the floor). Once the engine has warmed up, then tt is fine. If the outside temp is around 4/5 degrees C, then even this doesnt happen.

The ECU itself is a Bosch EDC15C2, and I have the print out from analyser from the last time it was looked at. It says:

Seems to me that there's either a specific wiring fault that can be corrected without changing the whole loom, or the ECU itself is toast and needs changing. (I'm thinking this might be the case due to the engines behaviour when very cold.)

However, Im no mechanic so Id be very grateful to hear from any body who might have experienced a similar problem, or of course any kind eprson who can offer me some advice. Thank you for reading this lengthy note, and thanks in advance to anyone who can help me.

That particular fault - code P0222/P1222? - is a common reoccurrence on most Pug HDi's. I take it from your detailed post that the "official" MAF sensor earth wiring modification that is supposed to cure it [but rarely does] has already been tried? A new twin pedal-sensor unit? Throttle cable correctly adjusted?

If so; then it will need a download of the latest edition of the software to even try and fix it; probably without much success. Why did they repeatedly replace this "fuel switch?" Was that a different - pressure-related - code?

Don't spend large amounts of your money on chasing it; Peugeot themselves don't seem to have a definitive answer. Just keeping it running until the secondary pump goes and then scrapping it is usually the best option on these. Many haven't made it as far as yours.

It's the one on the engine. The pump itself is around £700: it's the mandatory [warranty requirement] replacement of four electronic injectors, fuel lines, fuel-tank and primary pump, filter housing etc. that brings it up to around £2,500-£3,000.

Just broken the bad news to a C5 HDi owner on another forum. He's got metal frag in the filter at only 30,000 miles....

I've said it before - don't EVER own a "Common-Fail" diesel that's not covered by a bullet-proof warranty. Every single make are dropping like flies.

Thank you Screwloose for your thoughts. I didnt notice before but on the print out there's some handwritten text which says PO221 which I asusme is the fault code. It also says:

Pedal sensor 1 0%
Pedal sensor 2 0%
E SPEED 1189
Injector flow 0mm

if that helps at all...

As for changing the fuel switch, this was done by both garages as an attempt to remedy the fault. I recall once the light went out for a few days before coming on again, and once, after a wiring error had been corrected it was off for about three weeks...I can only assume that the s/w has been upgraded, but cant be certain.

By the way, what is a "CR" diesel engine... would you recomend any main stream manufacturer (Ford, Renault etc....) for their diesel engines? Or just go for any of them, and get a good warranty and then exchange the car when the warranty expires?

What was that "fuel switch?" There's no component of that name involved in the system. There's an inertia fuel shut-off switch; [a red square rubber object in the corner of the engine bay] and a fuel pressure sensor on the rail, but no switch...

One thing that's always worth checking on HDi's is the O-ring seal on the fuel-pressure control solenoid in the pump. Seen quite a few of those split.

Screwloose, thanks a million for taking the trouble to provide your input. You may have gathered, I am NO mechanic (my typing is not brilliant either...just re-read some of my comments!!)

So, "fuel switch" - ok, (sorry for the low tech description here) is the small wheel (visible, at the "top" of the engine) that the cable from the accelerator pedal passes "over" - I can only assume this is read via some electronics by the ECU to determine the speed of the engine - the more the foot is down on the gas pedal, the more the wheel is turned. Hope that helps.

Its been changed certainly twice, and I think three times. In each case the eng mgmt light has gone out, only to re-appear a few days later.

One seperate wiring mod made did extinguish the light for about three weeks as I recall but it came back on.

Interestingly, the car had its 84K service today and MOT. Cost me a bit to get it thru' the MOT but there we go. (13 months MOT always helps to sell a car ...) and the light is currently OUT! I'm about to do a 500 mile round trip in next few days so my guess is it will come back on. The garage didnt do anything that I could tell that would have caused it to go out. Car continues to drive well.

Interested in your advice on diesel engines. So, when thinking of my next car, a good, well tried and trusted petrol engine gets your vote then.

All now becomes clear. So this "fuel switch" is the twin track potentiometer better known as the accelerator pedal position sensor of P0221/222 fame! [Please don't ask me to explain why the accelerator pedal position sensor is hanging on the far end of a throttle cable and is nowhere near the accelerator pedal - it's just French OK!

Seeing that the whole of this fault is now neatly tied-in to that pair of sensors; I'd be inclined to start checking the earth potential between the battery negative, ECU earth, body earth, pedal sensor earth, MAF sensor earth and the main engine block earth etc. I'm wondering if the various earth voltages [there's always a little difference] are varying all over the place and upsetting the hyper-sensitive ECU.

Perhaps some equipotential bonding might be in order. The main earthing stud on these engines corrodes into the alloy clutch housing; you can't see it's done it until you completely remove the whole stud.

Thanks again Screwloose. The earth differences sounds very feasible (Im an Electronic Engineer by training so now I'm hearing something even I can understand!). Im half way thru' my 500 mile round trip, car is driving fine and the light is still out. Even today when I started the car for a short journey when it was 2 degrees outside - which up 'til now would have caused the engine to be extremely sluggish and non-responsive until it warms up - was fine.

I rang the garage who did the MOT work and service and we couldnt come up with anything that might have caused the light to go out. No wiring changes made or anything like that. However, the light might pop back on later.

I really appreciate the input here - thank you. By the way, I'd appreciate your thoughts on Hondas - I am thinking seriously of trading the Pug in for an Accord Tourer - seem to have good reliability record. I note the diesel engine is Hondas "first in house design" - any thoughts on this engine? Alternatively, I can get petrol version. Maybe a discussoin on Hondas would make a seperate "thread".

I spoke (well typed) too soon. After driving 100 metres yesterday there was a temporary drop in power and on came the light. It was late Sat night and outside temp very cold. Had front screen blower, rear heated screen and headlights on full so I guess current drain was pretty well near maximum. I'm wondering that given your comment on differeing earth potentials the high current would have made this worse thus upsetting the ECU.

Today drove the 250 miles home and light permanently stuck on, but car drives fine. Will investigate the earthing as you suggest. Many thanks. Howard

Using shielded cable from the signal wires of the throttle potentiometer to the engine ecu will greatly improve the fault you are getting, the fault is usually caused by interference from the injectors spiking the signal from the throttle pot as one of the tracks output starts at 0.4 volts it can be very easily corrupted by the 70 volt surge to the injetors. if you look at where the wires enter the ecu plug you will more than likely see the wires for the throttle pot run through the injector wiring.and by the way make sure the outer shielding of the cable is well earthed

Thankyou Brayer. I'm familiar with screened cable as I dabble with PA and recording! However, is there a more robust type of screened cable suitable for an engine environment, or is a decent quality audio screened cable suitable? If there's something more suitable, can you recommend where to get it from? Thanks again, I really appreciate the input from you and screwloose. Cheers, Howard.

Just an update. Following on from the excellent advice, (thanks to all of you who have helped) I had a guy who specialises in car electrical problems give the eng mgmt system and wiring a once over.

He said from what he could see that the wiring looked ok and was not damaged. Earthing was also ok. The engine management light is now out and has remained out since he did this analysis. (I can only assume that by removing power to the ECU resets its circuit and then all is ok). I only asked the guy to check the basics as it all costs money and the car is getting on a bit now.....

However, I suspect that if the outside temperature is very cold when I start the car then the light will come on, the car will behave in its usual erratic manner for a short while and then drive perfectly normally once the engine has started to warm up. I am of the opinion that either some sort of cold start circuit in the ECU is at fault, or the ECU itself has some sort of temperature compensation circuit and this is broken.

Hope this is of use to anyone else who may have a similar problem. Cheers, Howard

Quick update, the light came back on on Saturday 18th! Wasn't too cold (around +3 degrees) but its back on and has stayed on. Car continues to drive well. Pardon the pun, but given the wiring appears to be ok, I'm warming to the cold start circuit theory... any thoughts anyone? Thanks in advance. Howard

wish I knew Howard, but taking off the battery does indeed seem to reset the EMU. Before you do this is it worth having the system rescanned to see what fault codes now come up? I believe that the EMU does not store faults, so it needs to be scanned with the dash warning light still lit. Just a thought. I did come across a very specialist forum which others know about on here with a pretty amazing Pug specialist. Whilst I think it's out of order here to promote other places, it might help. FWIW I had 168k aout of my 406HDI110 with no probs until it bust a fuel return pipe & ran out of fuel. Was never the same after that.

The only observation I could have on low temps is either a dry joint contracting, or I think if it's really cold it does a kind of a glow-plug thing, but I don't know for sure. Can't wait to here what the real culprit turns out to be!
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